thermosphere: "write" placeholder code

thermosphere/src/start.s

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2019 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+ 
+/* For some reason GAS doesn't know about it, even with .cpu cortex-a57 */
+#define cpuactlr_el1 s3_1_c15_c2_0
+#define cpuectlr_el1 s3_1_c15_c2_1
+
+.section    .text.start, "ax", %progbits
+.align      3
+.global     _start
+.type       _start, %function
+
+_start:
+    // Disable interrupts
+    msr     daifset, 0b1111
+
+    // Set VBAR
+    ldr     x8, =__vectors_start__
+    msr     vbar_el2, x8
+
+    // Set tmp stack
+    ldr     x8, =__stacks_top__
+    mov     sp, x8
+
+    // Don't call init array to save space?
+    // Clear BSS
+    ldr     x0, =__bss_start__
+    mov     w1, #0
+    ldr     x2, =__end__
+    sub     x2, x2, x0
+    bl      memset
+
+    b       . // FIXME!
+
+.pool